Methods and systems for clocking a physical layer interface

ABSTRACT

A method for clocking a physical layer (“PHY”) and a controller of a computing device, comprises the steps of: generating a reference clock signal; synchronizing a plurality of clock signals as a function of the reference clock signal; and clocking the controller and the PHY using the plurality of synchronized clock signals.

CROSS REFERENCE

This application claims priority from a provisional patent applicationentitled “Apparatuses, Methods, and Systems Using Integrated Circuits”filed on Apr. 19, 2013 and having an Application No. 61/814,153. Saidapplication is incorporated herein by reference.

FIELD OF INVENTION

This invention generally relates to methods and systems for a physicallayer interface of a computing device and, in particular, to methods andsystems for clock generation and synchronization for a physical layerinterface of a computing device.

BACKGROUND

A physical layer of a computing device (“PHY”) is used for communicatingbetween integrated circuits and external devices, such as otherintegrated circuits, typically through a data bus or a set of signalwires. The physical layer is typically configured to implement a desiredcommunication protocol or specification that has been established forthe particular application.

FIG. 1a illustrates a diagram of a physical layer of the prior art forcommunicating between a memory controller and an external memory device.A standard double data rate (“DDR”) PHY 12 interacts with an on-chipmemory controller 10 and an off-chip dynamic random-access memory(“DRAM”) 22. The PHY 12 comprises a DDR physical layer interface (“DFI”)14, first-in-first-out (“FIFO”) buffers 16, and address and data macros18 for transmitting data between the FIFO buffers 16 and the DRAM 22.The memory controller 10 and the PHY 12 represent two primary designelements in DDR memory systems, which are used in virtually allelectronic system designs, from cellphones and set-top boxes, tocomputers and network routers.

The DFI specification defines an interface protocol between the memorycontroller 10 and the PHY 12, with a goal of reducing integration costswhile enabling performance and data throughput efficiency. The DFIprotocol defines the signals, timing, and functionality required forefficient communication across the PHY, which is known by a personhaving ordinary skill in the art and can be found at the followingwebpage http://www.ddr-phy.org. The DFI specification also allows thememory controller 10 to be operated at a same frequency as DRAM 12, orat half (or other fraction) of the frequency of the DRAM 12.

FIG. 1b illustrates a graph of clock signals for a physical layerinterface of the prior art. A CLK_CTL clock signal is inputted to thememory controller 10 from the clock generator 20 for clocking the memorycontroller 10. A CLK_MEM clock signal is inputted to the address anddata macros 18 of the PHY 12 for clocking the address and data macros 18to receive data from and/or transmit data to the DRAM 22. The CLK_CTLclock signal and the CLK_MEM clock signal are plotted side-by-side alonga time axis. The CLK_MEM clock signal can have twice (or anothermultiple of) the frequency of the CLK_CTL clock signal. Also, theCLK_MEM clock signal and the CLK_CTL clock signal are asynchronoussignals. Thus, there is uncertainty as to alignment of the clocksignals. Since the frequencies of the CLK_CTL signal and CLK_MEM aredifferent, the FIFO buffers 16 are needed to buffer any data to accountfor this asynchronous.

The depths of logic in the PHY 12 and in the memory controller 10 aredifferent, and, moreover, the logic may be operating at integralmultiple frequencies, which prove to be challenging during integration.The width of the PHY 12 makes it even more difficult to align the clocksignals, e.g., the CLK_CTL, CLK_MEM, and the CLK_DFI signal, for therespective logic and components.

Traditionally, the FIFO buffers 16 are employed to store data betweenthe memory controller 10 and the DRAM 22 in the PHY 12. The memorycontroller 10 writes data according to the CLK_CTL signal edge. The PHY12 can then read/write the data according to the timing of the CLK_MEMsignal. Based on the type of command, the PHY 12 can read data from theDRAM 22 or write data to the DRAM 22. A clock generator 20 generates theclock signals CLK_CTL, CLK_MEM, and CLK_DFI according to the operatingfrequencies of the memory controller 10, the DRAM 12, and according tothe DFI specification.

If a write command is given, the PHY 12 reads the data based upon theCLK_MEM signal, and routes the appropriate command and data. If a readmemory command is given, the PHY 12 reads the data based on the CLK_MEMsignal and sends the appropriate command and data. The PHY 12 also canread the data, sending an appropriate command, and wait for the datafrom the DRAM 22. Once the data is available, the PHY 12 writes the datato the FIFO buffers 16, and informs the availability of data to thememory controller 10.

There must be a significant number of FIFO buffers 16 in the PHY 12 toprovide reliable operation due to the frequency ratio of the CLK_CTL andthe CLK_MEM signals, and due to uncertainties between and among clockdistributions for the various components of the PHY 12. Additionally,the minimum latency for reliable operation needs at least threeadditional cycles of CLK_MEM due to a clock domain crossing, which willincrease the overall latency of the system and also increase the neededchip area. The depth of the FIFO buffers 16 also depends on thefrequency ratio and the skew between the clock signals from the clockgenerator 20.

Therefore, there exists a need to provide new methods and systems forproviding a PHY that can account for any frequency ratio, decreaselatency, and reduce the amount of chip area used for the PHY. Inparticular, there exists a need to provide new methods and systems for aPHY that do not need FIFO buffers between a memory controller and anexternal memory.

Additionally, the PHY must evenly distribute a reset signal and theclock signals throughout the PHY and the memory controller. In order tokeep the data in correct order, the reset signal must be simultaneouslydistributed throughout the memory controller and the PHY.

FIG. 7 illustrates a diagram of a distribution network of the prior artfor distributing clock and reset signals. Typically, a DDR data macrocan be 72 bits wide in depth, and 10 mm long in length. Due to itsrelatively extensive depth and length, clock distribution in the DDRmacro is challenging in itself, and further difficult when trying tosynchronize the signals for the DDR macro. Prior art uses twoindependent balanced distribution networks, one for a clock signal I_CLKand the other for a reset signal I_RESET.

The clock signal I_CLK is distributed to divider and counter blocks 30via a first distribution network 28. Simultaneously, a clock signalI_RESET is also distributed to divider and counter blocks 30 via asecond distribution network 26 to mirror the timing of when the I_RESETsignal is received by each of the divider and counter blocks 30.Unfortunately, the second distribution network 26 consumes a greatamount of chip area and consumes a great amount of power.

Therefore, there exists a need to provide new methods and systems fordistributing clock and reset signals to reduce the amount of chip areaused and to reduce power consumption for distributing the clock andreset signals.

SUMMARY OF INVENTION

An object of this invention is to provide methods and systems forsynchronizing clock signals used for a PHY and a memory controller of acomputing device.

Another object of this invention is to provide methods and systems forreducing latency for a PHY of a computing device.

Yet another object of this invention is to provide methods and systemsfor distributing clock and reset signals of a computing device, whichreduce chip area usage and power consumption.

Briefly, the present invention discloses a method for clocking aphysical layer (“PHY”) and a controller of a computing device,comprising the steps of: generating a reference clock signal;synchronizing a plurality of clock signals as a function of thereference clock signal; and clocking the controller and the PHY usingthe plurality of synchronized clock signals.

An advantage of this invention is that methods and systems forsynchronizing clock signals used for a PHY and a memory controller of acomputing device are provided.

Another advantage of this invention is that methods and systems forreducing latency for a PHY of a computing device are provided.

Yet another advantage of this invention is that methods and systems fordistributing clock and reset signals of a computing device are provided,which reduce chip area usage and power consumption.

DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, and advantages of theinvention can be better understood from the following detaileddescription of the preferred embodiment of the invention when taken inconjunction with the accompanying drawings in which:

FIG. 1a illustrates a diagram of a physical layer interface of the priorart between a memory controller and external memory device.

FIG. 1b illustrates a graph of clock signals for a physical layerinterface of the prior art.

FIG. 2a illustrates a diagram of the present invention of a physicallayer interface between a memory controller and memory.

FIG. 2b illustrates a block diagram for address and data macros.

FIGS. 3a-3b illustrate a diagram of the present invention forsynchronizing clock signals of a physical layer interface.

FIGS. 4a-4b illustrate a diagram of another embodiment of the presentinvention for synchronizing clock signals of a physical layer interface.

FIG. 5 illustrates a diagram of a clock generation and synchronizationblock of the present invention.

FIG. 6 illustrates a diagram for distributing reset and clock signalsacross an address macro of the physical layer of the present invention.

FIG. 7 illustrates a diagram of a distribution network of the prior artfor distributing clock and reset signals.

FIG. 8 illustrates a diagram of the present invention for distributingclock and reset signals.

FIG. 9 illustrates a graph of clock signals for a distribution networkof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the embodiments, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration of specific embodiments in whichthe present invention may be practiced.

Generally, the present invention provides methods and systems forsynchronizing various clock signals used in a PHY and a memorycontroller of a computing device. Synchronization can include phasealignment along the respective rising edges (or the respective fallingedges) of a plurality of signals to be synchronized. Thereby, the needfor clock domain crossing synchronization can be eliminated.

FIG. 2a illustrates a diagram of the present invention for interfacing amemory controller and an external memory via a PHY. A PHY 42 comprises aclock generator 50, a DFI block 44, and address and data macros 48 forcommunicating between the PHY 42 and a DRAM 22. The clock generator 50generates clock signals for clocking a memory controller 40, the DFIblock 44, and the address and data macros 48. For instance, the clockgenerator 50 generates an output signal O_CLK_CTL to the memorycontroller 40 and receives an input signal I_CLK_CTL from the memorycontroller 40. The output signal O_CLK_CTL is distributed throughout thememory controller 40 and can be routed back to the clock generator 50 asthe input signal I_CLK_CTL. Thus, the clock generator 50 can adjust andsynchronize the output signal O_CLK_CTL as a function of the inputsignal I_CLK_CTL, which can serve as a feedback signal.

Also, the clock generator 50 generates an output signal O_CLK_DFI to theDFI block 44 and receives an input signal I_CLK_DFI from the DFI block44. The output signal O_CLK_DFI is distributed throughout the DFI block44 and can be routed back to the clock generator 50 as the input signalI_CLK_DFI. Thus, the clock generator 50 can adjust and synchronize theoutput signal O_CLK_DFI as a function of the input signal I_CLK_DFI,which can serve as a feedback signal.

Furthermore, the clock generator 50 generates an output signal O_CLK_MEMto the address and data macros 48 and receives an input signal I_CLK_MEMfrom the address and data macros 48. The output signal O_CLK_MEM isdistributed throughout the address and data macros 48 and can be routedback to the clock generator 50 as the input signal I_CLK_MEM. Thus, theclock generator 50 can adjust and synchronize the output signalO_CLK_MEM as a function of the input signal I_CLK_MEM, which can serveas a feedback signal. The I_CLK_DFI signal and the I_CLK_MEM signal canbe at the same frequency. This frequency can be an integer divisor ofthe reference clock.

FIG. 2b illustrates a block diagram for address and data macros. Theaddress and data macros 48 can comprise an address macro and data macrosDM0-DM8. The address and data macros 48 provide analog circuitry for thePHY 42, including DLLs, drivers, etc. The address and data macros 48 canbe clocked by the clock generator 50.

FIGS. 3a-3b illustrate a diagram of the present invention forsynchronizing clock signals for a PHY and a memory controller of acomputing device. A phase locked loop (“PLL”) 60 generates a clocksignal that has twice the frequency (a “2×-clock”) of a system clocksignal of the computing device. The 2×-clock is distributed 62 withminimum skew between end points. The frequency of the 2×-clock of thePLL 60 is halved by a divider block 64 to generate a REF_PCK signal,which can be distributed to the memory device of the computing system(e.g., DRAM) via a driver 66. The REF_PCK signal can also be a primaryreference clock signal for synchronization of the other clock signals ofthe PHY and the memory controller of the computing device.

The 2×-clock can also be inputted to a divider block 68 to reduce itsfrequency by one half to generate a 1×-clock. The 1×-clock is theninputted to a MDLL 70. The MDLL 70 outputs various phase signals of the1×-clock, which are fed to a clock generation and synchronization block72 (“CGS 1”), a clock generation and synchronization block 86 (“CGS 2”),a clock generation and synchronization block 90 (“CGS 3”), and a clockgeneration and synchronization block 92 (“CGS 4”).

The output clock signal from the CGS 1 is distributed across the addressmacro via a distribution network 74. The CGS 1 also outputs the addressclock distribution signal (also referred to as “O_CLK_MEM signal”) via adistribution network 76. A CLK_AD (also referred to as “I_CLK_MEM”)signal at the end point of the distribution network 76 is fed back tothe CGS 1. The CGS 1 can then compare the CLK_AD signal with the REF_PCKsignal. The CGS 1 adjusts the output clock signals until the CLK_ADsignal is aligned to the REF_PCK signal. The aligned CLK_AD signal alsoacts as a reference clock to the rest of the CGS 2-4 to generate the PHYclock signals O_CLK_DFI and O_CLK_CTL.

Specifically, for the O_CLK_CTL signal, the generated output from theCGS 3 is inputted to a divider block 88 that can divide the frequency ofthe output signal from the CGS 3 by an integer value, e.g., by 1, by 2,by 4, or some other integer value. The controller clock signal O_CLK_CTLis fed to the memory controller, and further distributed across thememory controller. The end point of memory controller clockdistribution, i.e., I_CLK_CTL signal, can be fed back to the CGS 3 in afeedback loop. The I_CLK_CTL signal is compared with the CLK_AD signal.The CGS 3 adjusts the phase of the output clock O_CLK_CTL until theincoming I_CLK_CTL is synchronized with the signal CLK_AD.

Similarly, for the O_CLK_DFI signal, the generated output from the CGS 2is inputted to a divider block 84 that can divide the frequency of thegenerated output from the CGS 2 by an integer value, e.g., by 1, by 2,by 4, or some other integer value. The clock signal O_CLK_DFI is fed tothe DFI block of the PHY, further distributed across the DFI block. Theend point of the DFI block distribution can be fed back as the I_CLK_DFIsignal. The I_CLK_DFI signal is compared with the CLK_AD signal. The CGS2 adjusts the phase of the output signal O_CLK_DFI until the incomingI_CLK_DFI signal is synchronized to the CLK_AD signal.

The CLK_AD signal also clocks a flop 78, and the output of thedistribution network 74 clocks a flop 80. Data, from the memorycontroller of the computing device can flow serially starting at theflop 78, to the flop 80, and to a driver 82. The driver 82 outputs thedata for address, command, and control data to the memory device, e.g.,DRAM.

Since the data and addresses come from the memory controller or DFIblock, the data clock should be aligned to the address clock. The CGS 4provides synchronization of a dummy clock to the address clock. Theoutput clock generated by the CGS 4 is fed to a data macro dummy load 96via a distribution network 94. The end of the data macro dummy load, aDM_CLK signal, is compared with the CLK_AD signal. The DM_CLK signal isadjusted until the DM_CLK signal is in sync with the CLK_AD signal. Aconfiguration code O_PH_CTRL is preserved, and fed to the all the datamacros, e.g., DM0-8.

FIG. 3b illustrates a data macro DM0. The other data macros are similarto DM0 and are not shown, but would be apparent to a person havingordinary skill in the art. The active data macros DM0-8 receive abalanced 2×-clock, and send it through the respective slave DLL (“SDLL”)and CGS blocks with the configuration code preserved from the CGS 4. TheCGS 4 can be connected to the CGS's of the other data macros DM0-8 forproviding the configuration code.

For instance in DM0, the 2×-clock is distributed to a divider block 102.The divider block 102 divides the frequency of the 2×-clock by 2 togenerate a 1×-clock. The 1×-clock is outputted to the SDLL 104. The SDLL104 outputs a signal to the CGS 5. The CGS 5 generates a signal based onthe input from the SDLL 104 and the configuration code from CGS 4. Thegenerated signal of the CGS 5 is outputted to distribution networks 110and 108 for clocking flops 112 and 114. Data, e.g., from the memorycontroller, can flow serially starting at the flop 112, to the flop 114,and to the driver 116. The driver 116 outputs the signal DQ/DQS to thememory device, e.g., DRAM. Similarly, for the other DM1-8, the 2×-clockis distributed along with the configuration code in a similar manner forthose data macros.

It is understood by a person having ordinary skill in the art that thedata direction can be outgoing to the memory device as shown in FIG. 3b, as well as incoming from the memory device, which is not shown.Diagrams for receiving data from the memory device to the data macrosDM0-8 are not shown, but are readily apparent based on the presentdisclosure to a person having ordinary skill in the art.

Generally, a clock synchronization flow of the present invention can beas follows: (1) align the CLK_AD signal to the REF_PCK signal; (2) oncealigned, align all other clocks to the REF_PCK signal. In this way, thepresent invention can be immune to clock tree insertion delay (at leastto the first order), and does not require clock balancing between thememory controller, DFI block, and the address and data macros. Therebyintegration can be made simple and easier.

FIGS. 4a-4b illustrate a diagram of another embodiment of the presentinvention for synchronizing clock signals of a physical layer and amemory controller of a computing device. A clock delay computation canbe eliminated, including having to distribute a configuration codeacross the data macros 0-8. Here, clock synchronization can beaccomplished by using two clocks for synchronization. For instance, theCLK_AD signal can be synchronized to the REF_PCK signal and the rests ofthe clocks can be synchronized to the CLK_DM signal.

A PLL 140 generates a clock signal that has twice the frequency of asystem clock signal (also referred to as the 2×-clock). The 2×-clock isdistributed 142 with minimum skew between end points. The 2×-clock ofthe PLL 140 is divided and sent to DRAM to reduce clock jitter. Theclock going to the output buffer, i.e., REF_PCK signal, can be a primaryreference clock for synchronization of other clocks. The REF_PCK signalcan also be outputted to a memory device, e.g., a DRAM, via a driver148.

The 2×-clock has its frequency halved by a divider block 150 to generatea 1×-clock, which is then inputted to a MDLL 152. The MDLL 152 outputsvarious phase signals of the 1×-clock, which are fed to a clockgeneration and synchronization block 154 (“CGS 1 b”), a clock generationand synchronization block 166 (“CGS 2 b”), a clock generation andsynchronization block 170 (“CGS 3 b”), and a clock generation andsynchronization block 172 (“CGS 4 b”).

The output clock signal from CGS 1 b is distributed across the addressmacro via a distribution network 156. The end point of the clockdistribution CLK_AD is fed back to CGS 1 b. The CGS 1 b compares theCLK_AD signal with the REF_PCK signal. The CGS 1 b adjusts the outputsignal to the distribution network 156 until the CLK_AD signal isaligned to the REF_PCK signal. The output signal from CGS 1 b isoutputted to the distribution network 156, which further outputs to theaddress clock distribution. The distribution network 156 outputs to aflop 160 and feeds back the signal to the CGS 1 b. Data, from the memorycontroller of the computing device can flow serially starting at theflop 158, to the flop 160, and to a driver 162. The driver 162 outputsthe data for address, command, and control data to the memory device,e.g., DRAM.

The 2×-clock distribution can also be distributed to a divider block 174for dividing the frequency by half, which is then outputted to thedistribution network 176. A clock signal CLK_DM at the end point of thedistribution network 176 is outputted to a dummy load 178. The CLK_DMcan also act as a reference clock to the rest of the CGS 2 b-4 b togenerate the PHY clock signals O_CLK_DFI and O_CLK_CTL.

Specifically, for the O_CLK_CTL signal, the generated output from theCGS 3 b is inputted to a divider block 168 that can divide the frequencyof the output from the CGS 3 b by an integer value, e.g., by 1, by 2, by4, or some other integer value. The controller clock signal O_CLK_CTL isfed to the memory controller, and further distributed across the memorycontroller. The clock signal at the end point of the memory controllerclock distribution, i.e., the I_CLK_CTL signal, can be fed back to theCGS 3 b in a feedback loop. The I_CLK_CTL signal is compared with theCLK_DM signal. The CGS 3 b adjusts the phase of the output clockO_CLK_CTL until the incoming I_CLK_CTL is synchronized with the signalCLK_DM.

Similarly, for the O_CLK_DFI signal, the generated output from the CGS 2b is inputted to a divider block 164 that can divide the frequency ofthe generated output from the CGS 2 b by an integer value, e.g., by 1,by 2, by 4, or some other integer value. The clock signal O_CLK_DFI isfed to the DFI block of the PHY. The clock signal at the end point ofthe DFI block clock distribution can be fed back as the I_CLK_DFIsignal. The I_CLK_DFI signal is then compared with the CLK_DM signal.The CGS 2 b adjusts the phase of the output signal O_CLK_DFI until theincoming I_CLK_DFI signal is synchronized to the CLK_DM signal.

Since the data and addresses come from the memory controller or DFIblock, the data clock should be aligned to the address clock. The CGS 4b provides synchronization of a 1×-clock and the address clock. Theoutput clock generated by the CGS 4 b is distributed as the 1×-clock.The 1×-clock is inputted to a flop 158. The end of the data macro dummyload, a CLK_DM signal, is compared with the 1×-clock. The 1×-clock isadjusted until the 1×-clock is in sync with the CLK_DM signal.

FIG. 4b illustrates a data macro DM0. The other data macros DM1-8 aresimilar to DM0 and are not shown, but would be apparent to a personhaving ordinary skill in the art based on the present invention.

The active data macros DM0-8 receive a balanced 2×-clock and a balanced1×-clock for generating clocking signals for flops 211 and 214. Forinstance in DM0, the 2×-clock is distributed to a divider block 202. Thedivider block divides the frequency of the 2×-clock by 2 to generate a1×-clock. The 1×-clock is outputted to the SDLL 204. The SDLL 204outputs a signal to a CGS 5 b. The CGS 5 b generates a signal based onthe input from the SDLL 204. The generated signal of the CGS 5 b isoutputted to a distribution network 210 for clocking a flop 214. The1×-clock from CGS 4 b is outputted to a distribution network 208 forclocking a flop 212. Data, from the memory controller of the computingdevice can flow serially starting at the flop 212, to the flop 214, andto a driver 216. The driver 216 outputs the signal DQ/DQS to the memorydevice, e.g., DRAM. Similarly, for the other DM1-8, the 2×-clock and1×-clock are distributed in a similar manner for those data macros.

FIG. 5 illustrates a diagram of a clock generation and synchronizationblock of the present invention. A clock generation and synchronizationblock 240 can comprise a phase selection multiplexer 242, a phaseinterpolator (“PI”) 244, a controller 246, and a clock alignment block248. The clock alignment block can provide phase detection and falselock detection for inputted signals, REF_CLK and FB_CLK.

The phase selection multiplexer 242 selects two adjacent phases from aDLL's (e.g., MDLL's or SDLL's) phase outputs according to a controlsignal I_PH_CTRL. The control signal I_PH_CTRL can also control the PI244. Generally, the DLL outputs 8 phases to the multiplexer 242. Theselected two adjacent phases are interpolated by the PI 244 to generatea delayed clock O_CLK. The incoming clocks REF_CLK and FB_CLK areinputted to the clock alignment block 248, which generates up/downsignals to the controller 246 based upon whether the signals are phasealigned, and if that alignment is a false lock. For instance, the falselock detection compares the REF_CLK and FB_CLK, and generates a falsesignal when the REF_CLK and FB_CLK are out of phase. The controller 246reads the up/down signal from the clock alignment block 248, andgenerates I_PH_LOCK. Also, the O_PH_CTRL signal can be incremented ordecremented based on whether the REF_CLK signal is leading or laggingthe FB_CLK signal, and vice versa.

FIG. 6 illustrates a diagram for distribution of a reset signal andclock signals across an address macro of the physical layer of thepresent invention. A distribution network of the present invention candistribute a reset signal and clock signals to the PHY, and, inparticular, to the clock generator and the address and data macros. Forinstance, a reset distribution and clock signal distributions 300 aredistributed to the clock generator and the address macro. In particular,the reset and clock distributions are inputted to the dividers, CGS's,and the flops of the clock generator and the address macro.

FIG. 8 illustrates a diagram of the present invention for a distributionnetwork for clock and reset signals. In the address and data macros ofthe PHY, there are various divider and counter blocks that need to besynchronized to prevent scrambling data. The counters are aligned to thedata, such that data set A is sent first and then data set B is sentnext. The counter can be used to keep track of the order of each dataset.

The DDR PHY can employ counter and divider blocks 340 for proper datatransfer. The counter and dividers blocks 340 are spread over an area,e.g., an area of 10 mm^2. Any mismatch between the counter and dividerblocks 340 can either affect latency or can cause functional failure.Thus, careful distribution of the reset signals must be carefullydistributed in conjunction with a clock signal I_CLK.

The distribution network comprises a NAND gate 302, a counter 304,blocks 308 for transmitting the I_RESET signal, blocks 310 fortransmitting the I_CLK signal, and the divider and counters 340. Theblocks 308 and 310 can be buffers, amplifiers, or other devices forretransmitting an input signal.

Upon receiving a high signal for the I_RESET signal to signify a reset,the clock signal I_CLK can be gated off by the NAND gate 302 from beingdistributed to the distribution network of the blocks 310. The counter304 can count an M number of clock cycles before gating off the signal.

Upon receiving a low signal for the I_RESET signal to signify an end tothe reset, the clock signal I_CLK can be gated back on by the NAND gate302 after an N number of clock cycles from the point after receiving theend of the reset. The purpose of waiting the N number is to be sure thatthe reset signal has propagated to all of the divider and counters 340.Thereby, the reset signal I_RESET can be distributed as a normalasynchronous signal. The active edge of the reset signal I_RESET isprovided to the dividers and counters 310 to reset/initialize them.

FIG. 9 illustrates a graph for clock signals for a distribution networkof the present invention for distributing clock and reset signals. Sincethe clock distribution and reset signals are performed according to thepresent invention, all the divider and counters 340 begin counting atthe same, e.g., after N number of clock cycles from the end of theI_RESET signal.

While the present invention has been described with reference to certainpreferred embodiments or methods, it is to be understood that thepresent invention is not limited to such specific embodiments ormethods. Rather, it is the inventor's contention that the invention beunderstood and construed in its broadest meaning as reflected by thefollowing claims. Thus, these claims are to be understood asincorporating not only the preferred methods described herein but allthose other and further alterations and modifications as would beapparent to those of ordinary skilled in the art.

We claim:
 1. A method for clocking a physical layer (“PHY”) and acontroller of a computing device, wherein the PHY has an address macroand a double data rate physical interface (“DFI”), comprising the stepsof: generating one or more reference clock signals; synchronizing aplurality of clock signals as a function of the one or more referenceclock signals, wherein the address macro is clocked by a first clocksignal of the plurality of clock signals, wherein the first clock signalis synchronized to a certain one of the reference clock signals using afirst clock generation and synchronization block, wherein the controlleris clocked by a second clock signal of the plurality of clock signals,wherein the second clock signal is synchronized to the certain one ofthe reference clock signals using a second clock generation andsynchronization block, wherein the DFI is clocked by a third clocksignal of the plurality of clock signals, and wherein the third clocksignal is synchronized to the certain one of the reference clock signalsusing a third clock generation and synchronization block; and clockingthe controller and the PHY using the plurality of synchronized clocksignals.
 2. The method of claim 1 wherein the first clock signal isdistributed across the address macro and wherein the first clock signalis synchronized to the certain one of the reference clock signals usinga feedback signal from the address macro.
 3. The method of claim 2wherein the feedback signal is a clock signal at an endpoint of theclock distribution for the address macro.
 4. The method of claim 1wherein the second clock signal is distributed across the controller,and wherein the second clock signal is synchronized to the certain oneof the reference clock signals using a feedback signal from thecontroller.
 5. The method of claim 4 wherein the feedback signal is aclock signal at an endpoint of the controller clock distribution.
 6. Themethod of claim 1 wherein the third clock signal is distributed acrossthe DFI, and wherein the third clock signal is synchronized to thecertain one of the reference clock signals using a feedback signal fromthe DFI.
 7. The method of claim 6 wherein the feedback signal is a clocksignal at an endpoint of the DFI clock distribution.
 8. A method forclocking a physical layer (“PHY”) and a controller of a computingdevice, wherein the PHY has an address macro and a double data ratephysical interface (“DFI”), comprising the steps of: generating one ormore reference clock signals; synchronizing a plurality of clock signalsas a function of the one or more reference clock signals, wherein theaddress macro is clocked by a first clock signal (“O_CLK_MEM”) of theplurality of clock signals, wherein the first clock signal issynchronized to a certain one of the reference clock signals, whereinthe controller is clocked by a second clock signal (“O_CLK_CTL”) of theplurality of clock signals, wherein the second clock signal issynchronized to the certain one of the reference clock signals, whereinthe DFI is clocked by a third clock signal (“O_CLK_DFI”) of theplurality of clock signals, and wherein the third clock signal issynchronized to the certain one of the reference clock signals; andclocking the controller and the PHY using the plurality of synchronizedclock signals.
 9. The method of claim 8 wherein the first clock signalis distributed across the address macro, wherein the first clock signalis synchronized to the certain one of the reference clock signals usinga feedback signal (“I_CLK_MEM”), and wherein the feedback signal is aclock signal at an endpoint of the clock distribution for the addressmacro.
 10. The method of claim 8 wherein the second clock signal isdistributed across the controller, wherein the second clock signal issynchronized to the certain one of the reference clock signals using afeedback signal (“I_CLK_CTL”), and wherein the feedback signal is aclock signal at an endpoint of the controller clock distribution. 11.The method of claim 8 wherein the third clock signal is distributedacross the DFI, wherein the third clock signal is synchronized to thecertain one of the reference clock signals using a feedback signal(“I_CLK_DFI”), and wherein the feedback signal is a clock signal at anendpoint of the DFI clock distribution.
 12. A method for clocking aphysical layer (“PHY”) and a controller of a computing device, whereinthe PHY has an address macro and a double data rate physical interface(“DFI”), comprising the steps of: generating one or more reference clocksignals; synchronizing a plurality of clock signals as a function of theone or more reference clock signals, wherein the address macro isclocked by a first clock signal (“O_CLK_MEM”) of the plurality of clocksignals, wherein the first clock signal is synchronized to a certain oneof the reference clock signals, wherein the controller is clocked by asecond clock signal (“O_CLK_CTL”) of the plurality of clock signals,wherein the second clock signal is synchronized to a the certain one ofthe reference clock signals, wherein the DFI is clocked by a third clocksignal (“O_CLK_DFI”) of the plurality of clock signals, wherein thethird clock signal is synchronized to the certain one of the referenceclock signals, wherein the first clock signal is distributed across theaddress macro, wherein the first clock signal is synchronized to thecertain one of the reference clock signals using a first feedback signal(“I_CLK_MEM”), wherein the first feedback signal is a clock signal at anendpoint of the clock distribution for the address macro, wherein thesecond clock signal is distributed across the controller, wherein thesecond clock signal is synchronized to the certain one of the referenceclock signals using a second feedback signal (“I_CLK_CTL”), wherein thesecond feedback signal is a clock signal at an endpoint of thecontroller clock distribution, wherein the third clock signal isdistributed across the DFI, wherein the third clock signal issynchronized to the certain one of the reference clock signals using athird feedback signal (“I_CLK_DFI”), and wherein the third feedbacksignal is a clock signal at an endpoint of the DFI clock distribution;and clocking the controller and the PHY using the plurality ofsynchronized clock signals.